Steps:

1.Right-click on the operation you want to split and assign in parallel and select [Operation] – [Edit Operation…] from the popup menu.
2.Specify a value for the property “Split number” or “Split ratio” in the Split tab of the properties window.
3.Specify the number of resources to which you want to assign the split operations for the property “Split parallel number” in the Split tab of the properties window.
4.If you reschedule, the operation will be split and assigned according to the split number and split parallel number you specified.